Thermal decomposition of solid azobisisobutyronitrile

Abstract

The rate of the thermal decomposition of solid azobisisobutyronitrile was measured under conditions such that the side processes, such as gas-phase decomposition, the formation of liquid products, crystal cracking, and polymorphic transitions, had no effect on the process rate. The reaction occurs on the inner crystal surface, and its rate depends on the method of crystallization. The sample crystallized under conditions of low supersaturation is the most stable. The kinetic parameters of the reaction are E = 134.9 ± 3.5 kJ/mol and log A = 14.12 ± 1.5 [s−1]. The decomposition rate constant of solid azobisisobutyronitrile is 50 times lower than that of azobisisobutyronitrile in benzene solution. The low reaction rate in the solid phase is explained in terms of the additional-volume model proposed for unimolecular reactions in molecular crystals.